1. Field of the Invention
The invention relates to an alternating current electromagnet, and more specifically, to a design for a sideplate for securing a shading coil to a magnetic core of the electromagnet.
2. Description of the Prior Art
Alternating current electromagnets are wellknown. A typical application of an alternating current electromagnet is as an operating mechanism in an electrical contactor, such as a motor starter, where it is used to maintain the contacts of the electrical contact in a closed position.
A typical alternating current electromagnet has a magnetic assembly comprising a C-shape magnetic core forming two magnetic poles. An armature bridges these poles. A primary coil is arranged around each pole, and a 60 cycle alternating current is applied to the primary coil with the magnetic field collapsing 60 times per second. Springs in the electrical contactor tends to pull the armature away from the magnetic core, and therefore, the armature tends to oscillate with the magnetic field at 60 cycles per second. This condition causes noise in the system.
In order to reduce the oscillations, and thus the noise, a shading coil is provided in each pole face of the magnetic core. As is known to those in the art, a shading coil is a single turn, closed coil, and generally is mounted adjacent to the interface between the poles and the armature. Activation of the primary coil induces currents in the shading coil. These induced currents distort the magnetic field created by the primary coil, and change the time phase at which the alternating current goes to zero so that the magnetic field does not reach zero along the entire interface between the armature and the poles at the same instant, thereby reducing the extent of the oscillations of the armature.
In a typical alternating current electromagnet of the type discussed hereinbefore, the C-shape magnetic core is formed by two L-shape members which are either partially or totally separate from each other so that a gap exists to fix the inductance in the system. These L-shape members are typically comprised of several magnetic laminations or punchings and are interconnected by two C-shape sideplates, each attached on an opposed, parallel side of the magnetic core. An open channel in each of the pole faces of the core extends between these two sideplates, which in turn, have two slots, each cooperating with the channel in the two pole faces for receiving the shading coil. These two slots in each sideplate have a longitudinal opening which aligns with the channel in each pole face, such that in cross section the slots and the channel are in a C-configuration.
The shading coil is secured in the channel and slots by one of the well-known methods, such as by using an adhesive, or by staking, or by using a wire-form. In the staking method, the edges of the laminations or punchings of the core are upset along the channel in the pole face. In the wire-form method, a wire is looped over the shading coil, and a wire clip is used to secure the wire in place. This wire clip requires another slot or edge to bear against.
One of the major disadvantages of the prior art electromagnets is that several steps are required in assembling these electromagnets. First, the sideplates are attached to the core, and then the shading coil is attached to the pole face by one of the discussed methods. This two-step operation requires time and materials resulting in an increase in costs.
The adhesive method requires manual application of the adhesive, and a subsequent oven curing operation. Adhesive particles attach to the pole faces of the core, and in a grinding operation of the punchings to make the pole faces smooth, these adhesive particles may contaminate the coolant used in the grinding operation.